How can the Functioning of Treatment Wetlands be Enhanced?

Wetlands have already been recognized to hold the capacity for efficiently reducing or removing large amounts of pollutants from point sources (e.g. municipal and certain industrial effluents) as well as non-point sources (e.g. mining, agricultural and urban runoff) including organic matter, suspended solids, excess of nutrients, pathogens, metals and other micropollutants. This pollutants removal is accomplished by the interdependent action of several physical, chemical and biological processes which include sedimentation, filtration, chemical precipitation, sorption, biodegradation, and plants uptake among others. The mechanisms and the interdependences among the wetlands’ components (water, substrate and biota) are complex and not yet entirely understood, although some progresses have been achieved in the latest years as the awareness to the water depurative functions of wetlands becomes more widespread. In fact, studies have led to both a greater understanding of the potential of natural wetland ecosystems for pollutants assimilation and the design of new natural water treatment systems inspired in these natural systems, the constructed wetlands systems (CWS). These CWS can be defined as man-made systems that have been designed and constructed to utilize the natural processes involving wetland vegetation, soils, and their associated microbial populations to assist in treating wastewater. They are designed to take advantage of many of the same processes that occur in natural wetlands, but do so within a more controlled environment. However, until now these systems have been approached primarily as a “black-box”, without a thorough understanding of the processes involved. Ultimately, the optimization of CWS for the removal of more specific target compounds requires a basic knowledge of the processes involved in the removal of the pollutants and the interactions between those and the CWS components. New trends in CWS research are moving towards the study of such processes and interactions and focus on the selection and optimization of the CWS components for more specific applications. The aim of this work is to present a review on the main pollutant removal and transformation mechanisms in wetlands, the pollutants fate in the system and the roles played by the most important components of CWS (water, substrate and biota) in the processes and how they affect the overall treatment system performance. Some focus will be given to the most recent studies published on this subject especially those involving the treatment of micropollutants by CWS and the mechanisms that may be involved in the removal of these particular substances. Some of the questions remaining to be addressed about the removal mechanisms in CWS and the aspects of CWS operation that still require optimization will also be highlighted in this review

Studies On SONLO Properties Of Half-Sandwich Complexes Using TD-DFT Calculations

During the last decades there´s been a growing interest in the use of organometallic complexes as potential building blocks for second-order nonlinear optical (SONLO) materials, namely for photonics and integrated optics applications [1]. h5-Monocyclopentadienylmetal complexes are known to be good candidates for SONLO purposes. Systematic studies in these systems give the basis to predict that the combination of substituted acetylide thiophene chromophores with ruthenium and iron metal centers can enhance the first hyperpolarizabilitiy [2,3]. Also, it is well known that the first hyperpolarizability of purely organic push-pull molecules increases strongly with the length of the conjugated chain. Nevertheless, the exploitation of this effect in several h5-monocyclopentadienylmetal complexes showed contradictory results. The time-dependent density functional theory (TD-DFT) method within the DFT frame provides the satisfactory molecular orbital explanation for the electronic excitation, which is usually recommended for calculating the excited-state behaviours. In the case of organometallic complexes, the TDDFT method is one of the most suitable choices to calculate accurately the excited energy and first hyperpolarizabilities. In this work we used the TD-DFT method to study the first hyperpolarizabilities of [MCp(P_P)(CC{SC4H2}nY)] complexes (M=Ru, Fe; P_P= H2PCH2CH2PH2, DPPE; Y= CHO, NO2; n= 1,2) (Figure 1). The effect of the bidentate phosphine, different electron-withdrawing groups and the conjugated length of the chromophore will be evaluated. Our interest is not only to predict the β values but also to investigate the microscopic SONLO mechanism in these complexes

First Hyperpolarizability Of Some Nickel-Acetylide Complexes: A DFT Study

The search for new organometallic materials with second-order nonlinear optical (SONLO) properties is currently the subject of considerable interest due to their potential technologic applications in photonic devices for telecommunications and optical computing. Experimental systematic studies were made on half-sandwich complexes presenting nitrile and acetylide benzene and thiophene-based chromophores [1-3]. The results revealed that the combination of acetylide thiophene ligands with appropriate organometallic fragments would maximize the SONLO response. Also, recent TD-DFT studies on h5-monocyclopentadienyliron(II) complexes with substituted thienyl-acetylide ligands revealed the fundamental role played by the organometallic fragment on the corresponding SONLO properties [4]. In our continuous effort to get a better understanding on the electronic factors that may dictate the SONLO properties of η5-monocyclopentadienylmetal complexes with substituted thienyl-acetylide chromophores, we report herein the preliminary density functional theory (DFT) and time-dependent DFT (TD-DFT) results on the complexes [NiCp(PR3)(CC{SC4H2}nY)] (R=H, Ph; Y= CHO, CN, NO2; n=1,2) using the Gaussian03W program package. For instance, Figure 1 shows the optimized structure for NiCp(PH3)(CC{SC4H2}NO2. The effect of the phosphine, the Y-substituent and the conjugated length of the chromophore on the first hyperpolarizability will be evaluated. Some experimental spectroscopic data will be also explained on the basis of the TD-DFT calculations

Recent Developments in the Study of the Behavior of Fluorescent Membrane Probes in Lipid Bilayers: Molecular Dynamics Approach

We present a review of recent developments in the study of the behavior of fluorescent membrane probes in lipid bilayers by molecular dynamics simlations

Hydrothermal synthesis to water-stable luminescent carbon dots from acerola fruit for photoluminescent composites preparation and its application as sensors

Carbon dots (C-dots) possess the attractive properties of high stability, low toxicity, good water solubility, simple synthetic routes as well as size and excitation-dependent photoluminescence (PL).The aim of this work was to synthesize photoluminescent C-dots by hydrothermal method using acerola fruit (Malpighiaemarginata) as a row material, since this fruit contains large number of organic molecules. Studies about the optimal synthesis conditions were performed, where these organic molecules were converted into C-dots by hydrothermal carbonization at 180 ºC for 18 h. The C-dots exhibited a green emission light at 459 nm when excited under UV-light (λ ex= 370 nm). These nanomaterials were also successfully used to prepare C-dots/poly (vinyl alcohol) luminescent composites (C-dots/PVA). Both C-dots and C-dots/PVA composite films were investigated by using colorimetric visual sensor for Fe3+ metal ions detection. The results show that the prepared C-dots and C-dots/poly presented strong green emission light. The emission spectra of above materials were quenched in the presence of Fe3+ ions. Thus, highly specific “turn off” fluorescence sensing of Fe3+ was achieved using fluorescent C-dots. Regarding, this work describe that the polymeric films as sensors of metallic ions in aqueous solution appears as a new perspectives to design new composite materials22

The lateritic ore deposits of Brazil

Au Brésil, les mécanismes d'altération supergène ont conduit à la formation d'un épais recouvrement latéritique sur environ 65 % de la surface totale; dans des conditions particulières, l'accumulation de certains métaux dans ce manteau peut atteindre le stade économique. La latéritisation des diverses roches mères, tout à fait spécifiques de chaque type de gisement, est intervenue pour l'essentiel au Tertiaire, pendant des épisodes de stabilité tectonique auxquels correspondent des surfaces d'aplanissement généralisées. Le rôle des facteurs lithologiques, climatiques et morpho-tectoniques dans le mécanisme de genèse des gisements latéritiques est discut

Identification of vertebrate type steroid hormones in the shrimp Penaeus japonicus by tandem mass spectrometry and sequential product ion scanning

The identification of testosterone, pregnelonone, and 17α-hydroxyprogesterone by tandem mass spectrometry and of progesterone by sequential product ion scanning in the shrimp gonads of Penaeus japonicus is described. The identification of these substances in biological samples is usually done by gas chromatography-mass spectrometry and involves several liquid chromotographic purification steps followed by derivatization. The utilization of tandem mass spectrometry in this analysis has simplified considerably the sample pretreatment and provided a very simple method of screening these substances in complex mixtures